The question about TDMA surely as GSM adopted it.
TDMA uses 200 kHz per radio channel in comparison to analogue cellular allocations btw 12.5 kHz – 30 kHz. TDMA reduces the allocation each traffic channel to 200 kHz / 8 = 25 kHz, roughly equal to typical analogue system. This perhaps tell us TMDA lloked to some quality and features over simply increased capacity. I suppose to put use the same approach for use for analogue systems would require significant increase bandwidth for analogue systems making it inefficient to operate maybe?
GSM as I seem to remember want ‘efficency’ as spec’d at the outset to prove digital communications introduced an enhanced pan-european digital service over localised and diverse analogue systems.
Quality those has its price. TDMA structure gives more capacity (when compare with analogue). MS burst every 4.615ms has underlying freq 216.6 Hz (1/4615ms) which is an audible range and frequency can be heard on radio/music system speakers etc – so risks and nuisances need to be designed out but costs to do that.